@charset "utf-8";
.img-box{ width: 1024px; margin: 0 auto; }
#btn-top{ display: inline-block; width: 40px; height: 40px;
  background: url("../img/btn-top.png") 0 0 no-repeat; position: fixed;
  left: 50%; bottom: 60px; margin-left: 520px; display: none; }
#btn-top:hover{ background-position: 0 -40px; }